Amy

A mostly benevolent demon, Amy had an arrangement to possess the exterminator Lorne in exchange for leaving other people alone and behaving. 

His time on earth is a futile attempt at redemption, regretting having rebelled against heaven. He spends his time on earth sharing his vast knowledge on liberal arts and astronomy... By basically acting like a community college teacher.

He's a big nerd and loves talking about space. He'll always always try to clean up Lorne's apearance when he's in control but that doesn't last very long.